Gi alpha subunit
Chr. 7 q21-q22 | |||||||
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Chr. 3 p21 | |||||||
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Chr. 1 p13 | |||||||
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Chr. 16 q13 | |||||||
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Chr. 22 q11.22-11.23 | |||||||
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Chr. 3 p21.31 | |||||||
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Chr. 1 p13.3 | |||||||
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Chr. 7 q21.11 | |||||||
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Gi protein alpha subunit is a family of heterotrimeric G protein alpha subunits. This family is also commonly called the Gi/o (Gi /Go ) family or Gi/o/z/t family to include closely related family members. G alpha subunits may be referred to as Gi alpha, Gαi, or Giα.
Family members
There are four distinct subtypes of alpha subunits in the Gi/o/z/t alpha subunit family that define four families of heterotrimeric G proteins:
- Gi proteins: Gi1α, Gi2α, and Gi3α
- Go protein: Goα (in mouse there is alternative splicing to generate Go1α and Go2α)
- Gz protein: Gzα
- Transducins (Gt proteins): Gt1α, Gt2α, Gt3α
Giα proteins
Gi1α
Gi1α is encoded by the gene GNAI1.
Gi2α
Gi2α is encoded by the gene GNAI2.
Gi3α
Gi3α is encoded by the gene GNAI3.
Goα protein
Go1α is encoded by the gene GNAO1.
Gzα protein
Gzα is encoded by the gene GNAZ.
Transducin proteins
Gt1α
Transducin/Gt1α is encoded by the gene GNAT1.
Gt2α
Transducin 2/Gt2α is encoded by the gene GNAT2.
Gt3α
Gustducin/Gt3α is encoded by the gene GNAT3.
Function
The general function of Gi/o/z/t is to activate intracellular signaling pathways in response to activation of cell surface G protein-coupled receptors (GPCRs). GPCRs function as part of a three-component system of receptor-transducer-effector.[1][2] The transducer in this system is a heterotrimeric G protein, composed of three subunits: a Gα protein such as Giα, and a complex of two tightly linked proteins called Gβ and Gγ in a Gβγ complex.[1][2] When not stimulated by a receptor, Gα is bound to GDP and to Gβγ to form the inactive G protein trimer.[1][2] When the receptor binds an activating ligand outside the cell (such as a hormone or neurotransmitter), the activated receptor acts as a guanine nucleotide exchange factor to promote GDP release from and GTP binding to Gα, which drives dissociation of GTP-bound Gα from Gβγ.[1][2] GTP-bound Gα and Gβγ are then freed to activate their respective downstream signaling enzymes.
Gi proteins primarily inhibit the
Gz proteins also can link GPCRs to inhibition of adenylyl cyclase, but Gz is distinct from Gi/Go by being insensitive to inhibition by pertussis toxin.[5]
Gt proteins function in sensory transduction. The Transducins Gt1 and Gt2 serve to transduce signals from G protein-coupled receptors that receive
Receptors
The following G protein-coupled receptors couple to Gi/o subunits:
- Acetylcholine M2 & M4 receptors
- A3receptors
- α2Creceptors
- Apelin receptors
- Calcium-sensing receptor
- CB2[6])
- Chemokine CXCR4 receptor
- D4
- GABABreceptor
- mGlu8receptors
- Histamine H3 & H4 receptors
- MT3receptors
- HCA3
- μ, & nociceptinreceptors
- FP, & TPreceptors
- 5-HT5receptors
- FFAR3
- Somatostatin sst1, sst2, sst3, sst4 & sst5 receptors
- Trace amine-associated receptor 8
See also
- Second messenger system
- G protein-coupled receptor
- Heterotrimeric G protein
- Adenylyl cyclase
- Protein kinase A
- Gs alpha subunit
- Gq alpha subunit
- G12/G13 alpha subunits
- Retina
- Taste
References
External links
- Gi+alpha+Subunit at the U.S. National Library of Medicine Medical Subject Headings (MeSH)